Directional float tray



Aug. 25, 1964 J. FORGRIEVE 3,146,230

DIRECTIONAL FLOAT TRAY Filed Nov. 5. 1960 John Forgrieve INVENTOR PATENT ATTORNEY United States Patent 3,146,280 DIRECTIONAL FLOAT TRAY John Forgrieve, Chatham, NJ., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Nov. 3, 1960, Ser. No. 67,011 2 Claims. (Cl. 261-114) The present invention is concerned with an improved apparatus for countercurrently contacting liquids with vapors. More particularly, the invention is concerned with an improved fractionating tray whereby efficient contacting is obtained over a broad range of operation. In its particular aspects, the present invention is concerned with a fractionating device in which eflicient contacting is maintained over a broad range of liquid and vapor loadings by the use of floating tabs which are movably secured to the tray above vapor slots.

It is well known in the art to carry out separations wherein vapor and liquid are contacted on a fractionating tray. Normally the liquid passes from one tray to a lower tray by means of downcomers while the vapor passes upwardly from tray to tray through slots, chimneys, or caps into the liquid phase disposed on the tray.

The use of valve type slot covers dispersed on the tray which ride up and down above the vapor slots as the gaseous pressure beneath the tray changes is known in the art. Also, the use of stationary tabs which are inclined at an angle to the tray above vapor slots to impart a horizontal velocity component to the rising vapor in the direction of liquid flow is known to the art. Therefore, it is an object of the present invention to provide a simply constructed and assembled floating tab tray, so that the floating tab is inclined at an angle to the tray to impart a horizontal velocity component to the rising vapor in the direction of liquid flow across the tray.

The float valve trays presently known to the art consist of many parts such as a valve, ballast, and a means to retain the float valve and ballast on the tray. It is thus an object of the present invention to provide a directional floating tab of unitary construction which may be easily installed in the tray.

The directional jet trays have stationary tabs inclined at an angle to the tray, above vapor slots in the tray. The concept of the directional jet tray is that as the vapor rises through the slots, it is given a velocity component in the direction of liquid flow. The momentum interchange between vapor and liquid during phase contacting aids liquid in getting across the tray. As a result higher liquid rates are obtainable with the directional jet tray than with the conventional bubble cap tray. However, due to the fact that the tabs are stationary, the turndown ratio (the ratio of the maximum vapor rate at which satisfactory separation is obtained to the minimum vapor rate at which satisfactory separation is obtained) is approximately 2: 1. With the device of the present invention, turndown ratios of about 1620:1 are obtained. Performance such as this is far superior to any fractionating device currently known to the art.

The present invention is an improved fractionating device which provides efiicient vapor-liquid contacting over a broad range of vapor and liquid loadings by using an extremely simple contacting mechanism. In the present invention, vapor slots are punched from a sheet metal tray. Corresponding to each vapor slot is a tab which is also punched from sheet metal, and in the same punching operation is formed to the desired shape. The floating tab element is thus of one piece, or unitary construction. The floating tabs have the same shape as the vapor slots, but are slightly larger than the slots and overlap them.

The tabs are secured to the tray by means of guides which extend downwardly from the tab through the slots.

3,146,280 Patented Aug. 25, 1964 ice The lower extremity of each guide is formed outwardly from the tab and thus catches the underside of the tray and prevents the tab from being lifted from the tray. A tab is inserted in the tray by springing the guides inwardly to allow the lower portion of the guides to pass through the slot. The tab is then secured to the tray and is freely movable in a vertical direction within confined limits.

The present invention may be more fully understood by referring to the drawings, showing an embodiment of the present invention.

FIG. 1 is a top view of the floating tab as it appears on the tray when in the open position.

FIG. 2 is sectional view 22 through the floating tab in FIG. 1.

FIG. 3 is a top view of the floating tab illustrating its unltary construction.

FIG. 4 is a top view of a fractionating tray showing a floating tab layout.

Referring now to FIGS. 1 and 2 in more detail, numeral 1 represents a tray in which is punched slot 5. Tab 2 is slightly larger than slot 5 and overlaps slot 5 by about A 11:0 7 /s" preferred) at all points on its periphery except at the location of tab guides 3 where slight indentations are found to allow tab guides 3 to move freely in slot 5. The clearance between tab guides 3 and slot 5 is 4 to A /s" clearance for most services is satisfactory.

Tab guides 3 being 4 in number guide tab 2 in its vertical travel above tray 1. The lower extremity of each tab guide 3 is bent outwardly away from tab 2 to form lip 6 which restricts the upward movement of tab 2 above slot 5. Lips 6 extend to %g;", preferably /8", beyond the periphery of slot 5 under tray 1.

The length of the shortest tab guide 3, i.e. the .tab guide 3 located on the rear edge of tab 2, is to /2". This length is measured as the distance between the upper surface of lip 6 and the lower edge of tab rest 4. Thus the vertical travel of the rear edge of tab 2 is to /2". The preferred range is from about to A".

The length of the other three tab guides 3, i.e. the two on the side and the one on the forward edge of tab 2, should be such that tab angle B is in the range of from 5 to 45 The preferred tab angle B is about 20.

Tab rests 4, there being 4 in number, spaced at approximately equidistant intervals along the periphery of tab 2, keep tab 2 from making contact with tray 1. Tab rests 4 extend in the range of from to /2 below tab 2. The fractionating service for which tray 1 is to be used will determine the exact distance tab rest 4- extends below tab 2. For fouling service the distance will be greater than for non-fouling service.

The length of tab rest 4 is also determined with a view toward the directional feature of the present invention. The length of tab rests 4 is such that tab 2 will be inclined at an angle of at least about 5, even when the gaseous pressure beneath tray 1 is insufficient to lift tab' 2 from tray 1.

The cross-sectional area of slot 5 is from 0.25 to 9.0 square inches. The preferred cross-sectional area is in the range from 1-4 square inches.

FIG. 3 is an illustration of tab 2 with tab guides 3 and tab rests 4 as it is punched from sheet metal. The tab guides 3 and tab rests 4 are shown as they appear before bending them to their operating position. However, it is preferred .to punch and bend the tab in one operation. Slots 5 are punched in tray 1 and tab 2 may be installed on tray 1 by merely springing the tab guides 3 inwardly so as to allow lips 6 to pass through slot 5. Tab 2 will then pass freely up and down the distance between tab rests 4 and lips 6.

The action of floating tab 2 may be described by referring to FIGURES 2 and 4.

Liquid flows across tray 1 from the recessed inlet 8 toward downcomer 7. The purpose of recessed inlet 8 is to provide a liquid seal which prevents vapor from riding up the downcomer associated with the tray above.

Vapor rising upwardly passes through slot 5. As the gaseous pressure beneath tray 1 increases, tab 2 moves upwardly inclined at an angle B to tray 1. Thus, tab 2 moves upwardly to increase the vapor flow area until lips 6 contact the underside of tray 1. When tab 2 has reached its upward travel limit, the tab angle B is determined by the length of tab guides 3.

As shown in FIG. 4, there are many floating tabs 2 arranged in rows on tray 1 (the rows of tabs 2 being normal to the direction of liquid flow).

Adjacent rows of tabs are offset with respect to one another to avoid channeling of the liquid across tray 1. Channeling of liquid results in poor vapor liquid contacting because some tabs 2 are by-passed.

The distance between tabs 2 in one row is in the range of from about 1 to inches, and the distance between rows of tabs 2 is in the range of from about 1 to 5 inches.

The shape of tab 2 and slot 5 as shown in the figures is rectangular with a circular forward edge. While this is the preferred shape, other shapes which retain the basic features of the invention could be used.

As shown in FIG. 4, all of the floating tabs 2 are arranged in the same direction. By doing this liquid flow across the tray is aided.

However, with a small sacrifice in capacity an improvement in vapor liquid contacting may be obtained by reversing the direction of floating tabs 2 in every third or fourth row of tabs 2. In the reversed rows, the vapor is given a horizontal velocity component against the direction of liquid flow. This does impede the liquid flow across the tray to some extent, but advantages are obtained in the vapor-liquid contacting.

Also, the directional floating tabs 2 of the present invention may be used in conjunction with the conventional bubble cap or sieve tray contacting device.

One method is to have a number of rows of floating tabs 2 on the same tray with a number of rows of bubble caps.

Another method is to insert the floating tabs 2 only in selected vapor slots 5, leaving some vapor slots 5 open.

In these latter two instances, there is some sacrifice in liquid handling capacity. However, it is significant compared to the contacting advantages that can be obtained.

Having described the present invention, what is sought to be protected by Letters Patent is set forth in the following claims.

What is claimed is:

1. In a vapor-liquid contacting tray having a downcomer at one side thereof to provide liquid flow in a direction across said tray to the opposite side of the tray, said tray defining a plurality of spaced vapor slots arranged progressively in rows in the direction of said liquid flow and means providing a pressure head of vapor beneath said tray, the improvement comprising a generally horizontal flat tab disposed across and reciprocally movable in each slot in response to vapor flow through said slot, said tab having integral tab rest means of unequal length at opposite ends of the tab for resting against the upper surface of the tray and providing inclination thereof and escape of vapor in the direction of liquid flow upon a minimum vapor pressure head, said tab further having integral guides extending downwardly through said slots at opposite ends thereof downstream and upstream of liquid flow, each guide having at its lower end a stop to limit upward travel of the guide and the end of the tab attached thereto, the upstream guide being shorter than the downstream guide to provide limited upward travel of the upstream end of the tab and greater upward travel of said downstream end, whereby said tab may first travel upwardly for a predetermined distance in the inclined position generally determined by the tab rest means and thereafter the downstream end of the tab may swing upwardly through a greater angle with respect to the tray upon increasing vapor pressure.

2. The apparatus of claim 1 wherein said tab may be inclined at an angle of from 5 to to said tray, the

vapor slot has a cross-sectional area of from .25 to 9 square inches and the slots in adjacent rows in the direction of liquid flow are staggered across said tray.

References Cited in the file of this patent UNITED STATES PATENTS 2,061,830 Campbell Nov. 24, 1936 2,747,849 Colburn et al. May 29, 1956 2,809,821 Constantikes Oct. 15, 1957 2,853,281 Hibshman et a1. Sept. 23, 1958 2,979,316 Houston Apr. 11, 1961 2,982,527 Eld et al May 2, 1961 3,022,054 Kotzbue Feb. 20, 1962 3,080,155 Glitsch et a1. Mar. 5, 1963 FOREIGN PATENTS 803,711 Great Britain Oct. 29, 1958 OTHER REFERENCES Petroleum Refiner, vol. 39, No. 6, page 46, June 1960. 

1. IN A VAPOR-LIQUID CONTACTING TRAY HAVING A DOWNCOMER AT ONE SIDE THEROF TO PROVIDE LIQUID FLOW IN A DIRECTION ACROSS SAID TRAY TO THE OPPOSITE SIDE OF THE TRAY, SAID TRAY DEFINING A PLURALITY OF SPACED VAPOR SLOTS ARRANGED PROGRESSIVELY IN ROWS IN THE DIRECTION OF SAID LIQUID FLOW AND MEANS PROVIDING A PRESSURE HEAD OF VAPOR BENEATH SAID TRAY, THE IMPROVEMENT COMPRISING A GENERALLY HORIZONTAL FLAT TAB DISPOSED ACROSS AND RECIPROCALLY MOVABLE IN EACH SLOT IN RESPONSE TO VAPOR FLOW THROUGH SAID SLOT, SAID TAB HAVING INTEGRAL TAB REST MEANS OF UNEQUAL LENGTH AT OPPOSITE ENDS OF THE TAB FOR RESTING AGAINST THE UPPER SURFACE OF THE TRAY AND PROVIDING INCLINATION THEREOF AND ESCAPE OF VAPOR IN THE DIRECTION OF LIQUID FLOW UPON A MINIMUM VAPOR PRESSURE HEAD, SAID TAB FURTHER HAVING INTEGRAL GUIDES EXTENDING DOWNWARDLY THROUGH SAID SLOTS AT OPPOSITE ENDS THEREOF DOWNSTREAM AND UPSTREAM OF LIQUID FLOW, EACH GUIDE HAVING AT ITS LOWER END A STOP TO LIMIT UPWARD TRAVEL OF THE GUIDE AND THE END OF THE TAB ATTACHED THERETO, THE UPSTREAM GUIDE BEING SHORTER THAN THE DOWNSTREAM GUIDE TO PROVIDE LIMITED UPWARD TRAVEL OF THE UPSTREAM END OF THE TAB AND GREATER UPWARD TRAVEL OF SAID DOWNSTREAM END, WHEREBY SAID TAB MAY FIRST TRAVEL UPWARDLY FOR A PREDETERMINED DISTANCE IN THE INCLINED POSITION GENERALLY DETERMINED BY THE TAB REST MEANS AND THEREAFTER THE DOWNSTREAM END OF THE TAB MAY SWING UPWARDLY THROUGH A GREATER ANGLE WITH RESPECT TO THE TRAY UPON INCREASING VAPOR PRESSURE. 